fuel tank relocation

i am putting a 4-link on my 89 b2200 and i am wanting to move the tank behind the axle, but i am not sure where to mount the filler neck? i am still wanting to use the bed on this truck so i wasn't really wanting to put it inside the bed unless it can be mounted flush... ideas or pics would be great thanks!

GET RID OF YOUR SPARE TIRE CROSS MEMBER AND IT WILL FIT RIGHT INBETWEEN YOUR FRAME RAILSJUST EXTEND YOUR LINES. I GOT A CUSTOM FUEL CELL MADE UP SO THERE ARE PICS OF THE SPACE IN MY PROFILE CHECK IT OUT.